Silicone rubbers have excellent properties including high weatherability and electric properties, reduced compression set, and high heat resistance and cold resistance, and therefore, they are used in wide fields such as electric appliance, automobiles, construction, and foods. Applications include rubber contacts used in a remote controller, typewriter, word processor, computer terminal, musical instrument, and the like; gaskets used in construction; rolls used in copying machines, developing roll, transfer roll, charging roll, paper feed roll and other rolls; vibration control rubber in audio system; packings for compact disks used in computers. Demand for the silicone rubber is increasing, and development of silicone rubbers having improved properties are highly awaited. Silicone rubbers are generally provided in the form of a composition comprising an organopolysiloxane having a high degree of polymerization (starting polymer) and a reinforcing filler. This composition is prepared, for example, by mixing the starting polymer with the reinforcing filler and various dispersants using a mixer such as a kneader or a dual roll (roll mill).
As described above, in the production of the silicone rubber, a reinforcing filler should be kneaded in an organopolysiloxane, and a surface treating agent called “dispersant” is used in this process. When a silica is dispersed in an organopolysiloxane, the surface treating agent used is generally an organosilane or a siloxane having silanol group. Dispersion of the silica in the organopolysiloxane is a time consuming step, and there is an expectation for reducing the time required for the production by reducing the time used for the dispersion.
A straight chain organopolysiloxane having hydroxyl group at opposite ends is generally effective as a dispersant in producing the silicone rubber compound, and various dispersants have been used. Effectiveness and function of the dispersant depends on the content of hydroxyl group, and a polysiloxane having a higher content of the hydroxyl group, namely, a low molecular weight straight chain organosiloxane end capped with hydroxyl group can be used at a lower amount. Such polysiloxane is also more effective in view of the workability of the silicone rubber compound. For example, Japanese Patent No. 2853539 discloses a silicone rubber composition having 1,1,3,3-tetramethyldisiloxane-1,3-diol incorporated therein, and the resulting improvement of plasticity reversion and workability. However, commercial-scale production of the 1,1,3,3-tetramethyldisiloxane-1,3-diol is difficult and the price is accordingly high.
For example, Japanese Patent No. 2853539 discloses a silicone rubber composition having 1,1,3,3-tetramethyldisiloxane-1,3-diol incorporated therein, and the resulting improvement of plasticity reversion and workability. However, commercial-scale production of the 1,1,3,3-tetramethyldisiloxane-1,3-diol is difficult and the price is accordingly high.
Japanese Patent No. 2652307 discloses a method for producing a silanol having a relatively low molecular weight by using an alkoxysilane. This method requires neutralization with a metal oxide, removal of the methanol generated in the process.
JP-A 2004-189818 discloses a silicone rubber composition with reduced plasticity reversion. This document, however, does not describe addition of the water.